The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Photonic crystals (PC) are periodic dielectric structures with a band gap forbidding propagation of a certain frequency range of light. It is understood that controlling photon modes by PC structures can be useful. For example, electromagnetic waves can be bent with high efficiency around 90-degree corners within radii smaller than a wavelength with two-dimensional (2D) PC structures. Furthermore, a 3D PC can be used to control the timing of light emitted by a quantum dot. Moreover, a dual core photonic crystal fiber can be used for enhancing two-photon fluorescence biosensing sensitivity.
Selection from various types of PCs depends on specific applications. For example, 3D PCs are used in order to control spontaneous emission. In the case of controlling laser beams which are close to plane waves, a 1D PC is sufficient and preferable due to its simplicity in fabrication. Additionally, 1D PCs are used in various applications, such as an omnidirectional reflector, low-threshold optical switching, and nonlinear optical diodes.
Furthermore, a technique has been developed for enhancing fluorescence by sandwiching the sample of interest (e.g., chromophores) between two pieces of 1D PCs. When a structural defect is introduced in the PCs, a photon-localized state can be created in the photonic band gap and the electric field around the defect member is enhanced. In one embodiment, two-photon fluorescence emission from 2-aminopurine in the PC structure was enhanced by a factor of 120. However, the application of this approach is limited because the thick substrate of the PC structure inhibits the sample from being observed with an optical microscope or from interacting with other biomolecules.